Thread control in sewing machines is a very important consideration in the formation of a good stitch. In sewing machines employing oscillatory rocking loopers, a rotary thread take up mechanism is usually employed to manipulate the looper thread as demanded by the oscillatory, lengthwise movement of the looper. While the looper is moving toward the needle, the take up mechanism allows a certain degree of slack in the thread system to allow the previously formed stitch to be properly set. During the return movement of the looper, and once all the slack has been removed from the system, the take up mechanism is effective to pull or draw thread from the cone or supply source. Prior to the time the looper returns to its initial position, the looper thread will be "cast off" the high point of the looper thread take up cam. After the thread has been cast off from the thread take up cam, still further thread is delivered into the system between the take up cam and the looper because of the continuing return motion of the looper. It should be noted, the required amount of looper thread for the next stitch was also drawn into the system before the thread was cast off the high point of the take up cam.
When the looper thread breaks or becomes excessively loose, rotary thread take ups, particularly those of double disc design, tend to wind thread around and about the mechanism's operating shaft. Understandably, excessive thread wind up about the operating shaft will eventually inhibit machine operation. Thus, varying styles of thread break mechanisms have been designed to eliminate such problems.
U.S. Pat. No. 4,325,314 is but one example of a mechanism adapted to prevent looper thread wind up about an operating shaft. But even this latest technological development has certain drawbacks. The apparatus disclosed in U.S. Pat. No. 4,325,314 intermittently pinches the looper thread at a point between the looper thread take up mechanism and the thread supply source. The operation of this apparatus is such that should looper thread entanglement occur, this mechanism cuts off the supply of thread from the thread source whereby preventing excessive thread usuage and wind up about the operating shaft. This same device, however, has the disadvantage of drawing additional unwanted looper thread during the stitch forming cycle. The provision of such an apparatus also requires the looper thread to pass through yet another thread handling instrumentality. The problematical thread handling effects of such an arrangement are apparent. Moreover, such a mechanism is not effective during the entirety of the stitch forming cycle. As mentioned, such device is only intermittently operated. Even with the patented apparatus, a small portion of looper thread will become wound about the operating shaft before the thread breaks. Eventually, these thread pieces will windingly accumulate about the shaft. Before the machine is returned to operation, this wound thread must be removed from the shaft to enable use of the machine. In many machines, the thread take up area is inaccessible. Thus, the problem of removing the wound thread from about the rotary shaft is a timely and costly process.
The present invention involves a thread control mechanism which has the advantage of preventing thread from becoming wound about the operative mechanism of the machine. To accomplish these ends, the present invention includes a pneumatic apparatus which is arranged in combination with the thread take up mechanism and is operated coincident with operation of the machine for preventing excessive or broken ends of thread from becoming entangled with the operative mechanism of the machine. More particularly, the present invention includes means for directing a fluid medium against the looper thread and in a direction away from the operative components of the machine whereby excessive thread or thread ends are displaced from the operative environment of the machine. Thus, excessive thread wind up about an operative shaft is eliminated.
In line with all of the above, it is the primary object of this invention to provide suitable means which will prevent thread from spooling up about the thread take up mechanism of the machine.
It is another object of this invention to provide a thread control mechanism which is relatively simple in construction, dependable in operation, and is suited for use in connection with industrial sewing machines.
Yet another object of this invention is to provide a thread control mechanism which is versatile for use with machines regardless of the degree of looper travel.